Peter R. Rizun is a physicist and entrepreneur living in Vancouver, Canada, and is co-founder and co-managing editor for Ledger. His main research interest is developing analytical theory that explains properties and emergent phenomenon of the Bitcoin Network. He was the recipient of the $105,000 Natural Sciences and Engineering Research Council (NSERC) CGS Doctoral Award and was recognized as a “Leader of Tomorrow” by the Alberta Science and Technology Foundation (ASTech). He holds a B.A.Sc. degree in Engineering Physics from the University of British Columbia and a Ph.D. in Medical Physics from the University of Calgary.

Subchains: A Technique to Scale Bitcoin and Improve the User Experience

Peter R. Rizun

Abstract

Orphan risk for large blocks limits Bitcoin’s transactional capacity while the lack of secure instant transactions restricts its usability. Progress on either front would help spur adoption. This paper considers a technique for using fractional-difficulty blocks (weak blocks) to build subchains bridging adjacent pairs of real blocks. Subchains reduce orphan risk by propagating blocks layer-by-layer over the entire block interval, rather than all at once when the proof-of-work is solved. Each new layer of transactions helps to secure the transactions included in lower layers, even though none of the transactions have been con-firmed in a real block. Miners are incentivized to cooperate building subchains in order to process more transactions per second (thereby claiming more fee revenue) without incur-ring additional orphan risk. The use of subchains also diverts fee revenue towards network hash power rather than dripping it out of the system to pay for orphaned blocks. By nesting subchains, weak block verification times approaching the theoretical limits imposed by speed-of-light constraints would become possible with future technology improvements. As subchains are built on top of the existing Bitcoin protocol, their implementation does not require any changes to Bitcoin’s consensus rules.

Rizun, P. R. “The marginal cost of adding another transaction to a block is nonzero: empirical evidence that bigger blocks are more likely to be orphaned.” Reddit (16 July 2016) https://www.reddit.com/r/btc/comments/4t6guk/the_marginal_cost_of_adding_another_transaction/